Generally, pillows are employed, but it is not possible in that way to have a sufficiently stable supporting form.
It may furthermore be desired to have lateral arms or shelves the presence of which, as well as the presence of supporting elements for the human back, must be removable in order to use the bed for sleeping.
The use of sofa-beds, besides, requires that in the sofa position a longitudinal back be provided at a distance from the front edge of the sofa-bed which is substantially narrower than the width required for a comfortable bed.